1. Field of the Invention
The present invention relates in general to power level monitors for nuclear reactors; and more particularly, to power level monitors which detect neutron emissions from a pressurized light water nuclear reactor.
2. Description of the Related Art
Several types of radiation detectors are used in the monitoring of nuclear reactors. One type detects gamma radiation from, e.g., power generation/cooling loops. Other radiation detectors sense the emission of neutrons from, e.g., the core barrel which surrounds the reactor. The neutron sensors are typically one of two types, the first type is used to detect infrequent emissions during low level operation of the reactor, such as during the start-up of the reactor in what is termed the source range. The second type of neutron sensors, for example dual uncompensated ionization chambers, such as WL-24156, manufactured by Westinghouse Industrial & Government Tube Division, detect more frequent emissions of neutrons in intermediate and power ranges.
The signals output by the second type of neutron sensors include flow induced perturbations or "nuclear noise", particularly in the power range, caused by vibration of the core barrel generated when water from the cooling loops enters the core barrel.
A prior art circuit for monitoring the power level of a nuclear reactor by detection of neutron emissions is illustrated in FIG. 1. The neutron sensors 10 are of the second type, described above, and output a current which indicates the number of neutrons detected during a sampling period. A current-to-voltage amplifier 15, such as an NM310 summing and level amplifier (part no. 3378C21), manufactured by Westinghouse Electrical Systems Division, converts the current signal to a voltage signal which is supplied to a rate/lag circuit 20, such as an NM311 power range rate circuit (part no. 3378C20), manufactured by Westinghouse Electrical Systems Division. The rate/lag circuit 20 is represented by an amplifier 25 having one input directly receiving the voltage from the current-to-voltage amplifier 15 and another input receiving the voltage signal filtered by an RC circuit comprising a variable resistor 30 and capacitor 35; however, a typical rate/lag circuit will include additional elements.
Proper adjustment or alignment of the prior art power level monitoring circuit illustrated in FIG. 1 requires the generation of known input signals, adjustment of the rate/lag circuit 20 by, e.g., changing the resistance of the variable resistor 30. Next, additional adjustments are made to circuits (not shown) which receive the output of the rate/lag circuit 20. In practice, the alignment of the rate/lag circuit 20 has been found to be quite difficult, sometimes requiring reiterative adjustment of the rate/lag circuit 20 and the following circuits. In addition, the noise filtering capability of prior art power level monitoring circuits has been limited to removing some high frequency signals. Also, the use of an RC network in the rate/lag circuit 20 results in relatively slow response for prior art power monitoring circuits, making quick detection of transients difficult.